Description

In the spring of 1868, the Sierra Nevada were finally "conquered" by the Central Pacific Railroad after almost five years of sustained construction effort with the successful completion at Donner Pass of its 1,659-foot (506 m) Tunnel #6 (aka the Summit Tunnel) and associated grade thus permitting the establishment of commercial transportation en masse of passengers and freight over the Sierras for the first time. Following a route first surveyed and proposed by the CPRR's original Chief Engineer, Theodore D. Judah (1826â€“1863), the construction of the four tunnels, several miles of snowsheds, and two "Chinese Walls" necessary to breach Donner Summit constituted by far the most difficult engineering and construction challenge of the entire original Sacramento to Ogden CPRR route.

Principally designed and built under the personal, often on-site direction of the CPRR's Chief Assistant Engineer, Lewis M. Clement (1837â€“1914), the original (Track 1) summit grade remained in daily use from June 18, 1868, when the first CPRR passenger train ran through the Summit Tunnel, until 1993 when the Southern Pacific Railroad (which operated the CPRR-built Oakland-Ogden line until its 1996 merger with the Union Pacific Railroad) abandoned and pulled up the 6.7 mile (10.7 km) section of Track #1 over the summit running between the Norden complex (Shed 26, MP 192.1) and the covered crossovers in Shed #47 (MP 198.8) about a mile east of the old flyover at Eder. Since then all East and Westbound traffic has been run over the Track #2 grade crossing the summit about one mile (1.6 km) south of Donner Pass through the 10,322-foot (3,146 m) long Tunnel #41 (aka "The Big Hole") running under Mt. Judah between Soda Springs and Eder. Then operator SPRR made this change because the railroad considered Track 2 and Tunnel 41 (which was opened in 1925 when the summit section of the grade was finally double tracked) to be far easier and less expensive to maintain and keep open in the harsh Sierra winters than the Track 1 tunnels and snow sheds over the summit.
Donner Lake (left) and the now abandoned original CPRR (later SPRR Track 1) grade over Donner Pass. The Lincoln Highway can be seen in the middle of the photo, climbing the pass, to the left of the railroad bed.

In conjunction with major ongoing upgrades and expansions being made to the Port of Oakland in order to better accommodate the rapidly growing North American trade with Asia and the Pacific, the cooperation of the UPRR, the Port's principal rail partner, has been sought to "construct a second track and raise tunnel clearances over Donner Pass for container trains linking California with the rest of the country." This would likely require either a new parallel tunnel next to Tunnel 41 or the replacement of the summit section of Track 1 between the Norden complex and Shed 47; either would increase capacity and effectively eliminate delays currently caused by having to run all east and west bound traffic between Norden and Shed 47 over a single track. (To fully eliminate "bottleneck" delays the now single track 7.1-mile (11.4 km) section between Switch 9 (MP 171.9) and Shed 10 (MP 179.0) west of Cisco would likely also have to be restored to double track.) Improvements were completed on the Sierra grade in November 2009, including increasing 18,000 lineal feet of tunnel clearances in 15 restricted tunnels between Rocklin and Truckee and upgrading 30 miles of signals to CTC, although the original Donner Pass grade (Track 1) was not restored. Since then trains of full-height (20 ft 2 inch) double-stack container cars have run over Donner Pass; some tunnels on Track 2 between Bowman and Colfax were not enlarged, so stack trains in both directions must use the older, tunnel-free Track 1 between those points.